Both for comfort and security, motor vehicles are increasingly provided with central processor control systems for the electrically-operated components, including, especially, the antitheft warning system and the various components also mentioned above.
For example, with a computerized system the electrical components can be set to accommodate various drivers of the vehicle to permit the components such as the seat setting and mirror setting to be established for each individual likely to drive the vehicle. Other components which can be controlled through the central processor, can include interior lighting, trunk lighting, heatable rear windows and the like.
Prior to the advent of central processor controls, i.e. in classical electrotechnical wiring of motor vehicle harnesses, each of the vehicle components, including the respective actuating elements such as switches, push buttons or the like, were wired separately.
The number of components and control elements, wires and the like was, therefore, substantial and the cost of the wiring system was very high. In addition, reliability of the electrical system fell with increasing complexity and the cost of repair and maintenance was high as well.
Utilizing a central processor and a control system in which the central processor could operate a multiplicity of the vehicle components through a bus arrangement, a service person was able to maintain the system more simply and the system allowed actuation and initiation of the various functions through the central processor. In this case, the actuation of the various components is effected in a manner similar to the manipulation of a keyboard of a computer.
The use of satellite processors, however, permits local electrical actuators to be used as well and is especially advantageous in the case of window lifters and the like. When satellite processors are used, they are generally provided close to or in the vehicle components which they are intended to control. The satellite processor can be provided to operate only a single vehicle component or a number of vehicle components. Furthermore, each satellite processor can be designed to enable a single function to be carried out or to allow one or more vehicle components to have various functions carried out therein. In the case of a vehicle door lock, for example, the locking, unlocking, antitheft securing, disconnection of the antitheft mode, opening of the latch and even the function of drawing the door tight, may be automatically performed by, for example, electric motors connected to the door lock system under the control of the satellite processor.
With complex control functions of this type, especially in the case of vehicle door locks, the vehicle components, for example, the levers and links of the door lock system, can be provided additionally with sensors, especially Hall-effect position sensors, whereby the actual positions of the elements of the components can be determined and which can be connected to the respective satellite processor.
A multiplex single-conductor bus, as mentioned previously, is a system for the serial transmission of digital information which requires only a single conductor connecting the central processor with satellite processors, usually via respective branches, utilizing digital signals which, as a rule operate as pulse-width-modulation. It is possible utilizing a multiplex single-conductor bus to eliminate the need for a separate so-called clock line, the counterpole for the conductor of the multiplex single-conductor bus is the vehicle ground or chassis ground. Of course it can also be a ground line, for example, a shield for the bus conductor.
Apart from the multiplex single-conductor bus, only a current supply line need be connected to the motor-vehicle component.
Mention above of a master signal is intended to designate a signal delivering digital information which effects an activation or deactivation of a motor vehicle component. A control signal, then, is a signal which provides digital information as to the status of a motor-vehicle component or is an error-control signal for feeding back of the occurrence of an incomplete action or operation or a failure in the activation or deactivation. To the extent that such signals are transmitted in both directions between satellite processors and the central processor, the multiplex single-conductor bus is considered to provide a bidirectional dialogue between the processors.
A method of the aforedescribed type is found in EP-O 470 056 A2. In that system, the central processor is operated as the "master" while the satellite processors operate as "slaves." The "master" issues master signals or control signals which are transmitted over the multiplex single-conductor bus. A "slave" can only issue master signals or control signals which are transmitted over the multiplex single-conductor bus when it is interrogated by the master and thus is "enabled" by the master to issue such signals.
The earlier process operates address-free, i.e. master signals or control signals are not especially directed to the central processor or to one of the satellite processors. On the contrary, each satellite processor has an interface circuit through which the single-conductor bus is connected to that satellite processor. A first interface circuit permits master signals or controls signals to reach a second subordinate interface circuit only after the satellite processor associated with the first interface circuit has carried out certain routines. The processing continues with this hierarchical operation. Thus the satellite processors are not parallel to one another as same-rank units which are connected to the multiplex single-conductor bus.
The earlier process is thus comparatively slow and, when attempts are made to operate it by utilizing higher operating frequencies, the system tends to become unreliable. Significant time may be necessary in such systems before a lower ranked satellite processor, comparatively distal to the central processor, may be used for activation of the respective vehicle component.